1. Field of the Invention
The present invention relates to an optical ring network and, in particular, to a configuration of nodes provided in an optical ring network.
2. Description of the Related Art
A recent explosive growth in the Internet traffic demands a higher bandwidth for all networks including the backbone of an optical network, which is based on a Wavelength-Division-Multiplexing (WDM) scheme. The optical ring network is a network topology that is attracting considerable attention due to its easy configuration, switching restoration, lower initial costs, and so forth, and it has been already adopted in many countries.
In general, an optical ring network must provide a full-mesh connectivity between all nodes that constitute the network. Currently, the optical ring network generally makes use of not only a multi-wavelength for WDM on the basis of two or four strands of optical fibers but also employs an approach where each pair of the nodes is connected to form optical paths. With an escalating growth in data traffic, the transmission capacity required for most networks is increasing, and a possibility of a shortage in transmission capacity is great. However, in terms of an efficiency of a metro network, a two-fiber network is expected to have a higher efficiency than a four-fiber network. For this reason, the two-fiber network is attracting more attention than the four-fiber network.
The optical ring network may be generally classified into two classes: a unidirectional-wavelength-path-switching ring (UWPSR) and a bidirectional-fiber-line-switching ring (BFLSR). However, both a UWPSR and a BFLSR require many optical channels to accomplish a full-mesh connectivity in the network. To overcome this problem, a bidirectional-wavelength-path-switching ring (BWPSR) has bas been introduced.
In a BWPSR, there is an advantage in that it is capable of performing a rapid restoration under the protection and restoration condition and comprises a simple configuration. However, there are some drawbacks in that a BWPSR limits the number of nodes that can be adapted, thus the whole transmission capacity of the network is reduced as an excessive number of optical channels must be connected to all the nodes. In addition, each optical fiber is provided with a wavelength-division multiplexer in which the number of ports corresponds to that of WDM channels, thus each node requires switches for as many channels as are added or dropped. Furthermore, during the switching mode, a BWPSR needs a longer time to perform the switching restoration operation.
In a BFLSR, there is an advantage in that a number of optical channels is less, but there are disadvantages in that it has poor compatibility with the existing equipments, such as a synchronous optical network (SONET), and the number of desired wavelengths is more than that of a BWPSR. Further, a BFLSR demands a large number of wavelength-division multiplexers, such as arrayed waveguide grating (AWG), for 32 ports when it makes use of 32 channels.
As such, in all the cases mentioned above, a wavelength-division multiplexer is required when the network has as many ports as WDM channels. In the field of a wavelength-division multiplexer, an increase in the port means that both the cost of a wavelength-division multiplexer and the number of components connected with each port are increased, thus increasing expenses for configuring each node.